LTM4600 LINER [Linear Technology], LTM4600 Datasheet - Page 17

• Manufacturer Part Number: LTM4600
• Description: 10A High Effi ciency DC/DC ?Module
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Layout Checklist/Example
The high integration of the LTM4600 makes the PCB board
layout very simple and easy. However, to optimize its electri-
cal and thermal performance, some layout considerations
are still necessary.
• Use large PCB copper areas for high current path, in-
• Place high frequency ceramic input and output capaci-
• Place a dedicated power ground layer underneath
• To minimize the via conduction loss and reduce module
• Do not put via directly on pad
• Use a separated SGND ground copper area for compo-
Figure 16 gives a good example of the recommended
layout.
cluding V
PCB conduction loss and thermal stress
tors next to the V
high frequency noise
the unit
thermal stress, use multiple vias for interconnection
between top layer and other power layers
nents connected to signal pins. Connect the SGND to
PGND underneath the unit
C
IN
V
PGND
IN
Figure 16. Recommended PCB Layout
IN
, PGND and V
LOAD
U
IN
V
, PGND and V
OUT
U
TOP LAYER
OUT
. It helps to minimize the
W
OUT
pins to minimize
SGND
4600 F16
U
Frequency Adjustment
The LTM4600 is designed to typically operate at 800kHz
across most input and output conditions. The f
typically left open or decoupled with an optional 1000pf
capacitor. The switching frequency has been optimized for
maintaining constant output ripple noise over the operating
ranges. The switching frequency will increase up to typically
1.2MHz for 5V and 3.3V outputs to limit increase output
ripple noise. The switching frequency can be adjusted
lower to accommodate high duty cycle requirements like
5V to 3.3V, and 12V to 5V. There are limitations to input
voltage range for the higher duty cycle designs that limit
the internal inductor ripple current so that the inductor will
not saturate at higher load current. Examples:
Equations for setting frequency:
t
1MHz frequency or 1µs period is chosen for 12V to 5V.
t
band.
Using the frequency = (I
I
calculated from 12V input was 103µA, so a resistor from
f
57µA, sets the adequate I
range for the higher duty cycle conversion of 12V to
5V. Input voltage range is limited to 9V to 16V. Higher
input voltages can be used without the 15k on f
OFF
ON
ON
ADJ
LTM4600 minimum on-time = 100ns
LTM4600 minimum off-time = 400ns
I
frequency = (I
duty cycle is (V
t = t
switching period; t = 1/frequency
t
t
t
ON
ON
ON
OFF
and t
= (1MHz • 2.4V • 10pF) • (1/0.41) ≅ 58µA. I
must be greater than 400ns, or t – t
to ground = (0.7V/15k) = 46µA. 103µA – 46µA =
= V
= DC • t
= 0.41 • 1µs ≅ 410ns
= 1µs – 410ns ≅ 590ns
ON
OFF
IN
+ t
are above the minimums with adquate guard
– 0.7V/110k; for 12V input, I
OFF
ON
, t
OUT
ON
/[2.4V • 10pF]) • DC; DC = duty cycle,
/V
= on-time, t
IN
ON
ON
)
/[2.4V • 10pF]) • DC, solve for
current for proper frequency
OFF
LTM4600
= off-time of the
ON
ON
> 400ns.
= 103µA
ON
ADJ
ADJ
17
current
pin is
. The
4600fa